I’ve never done it, but it might depend entirely on the VI system being used. If it’s the kind that asks you consecutive questions with only a few seconds pause in between to read the next question then this might not be feasible on a mobile device (be it front or rear camera). You won’t be able to read the question if you are using the rear camera or it might be too small to see using the front.
If the VI system just requires you to record video clip answers to set questions then it sounds feasible to use a mobile device. Although all the VI’s I’ve done were of the former variety.